The invention pertains to a method for adjusting the rolls of a roll stand, wherein the roll stand comprises at least two cooperating work rolls, wherein one of the work rolls is mounted movably in the roll stand for adjusting the roll gap, and wherein the other work roll in the roll stand is mounted rotatably in a working position but is held fixedly in the direction perpendicular to the surface of the in-process stock for defining a pass line. The invention also pertains to a roll stand with at least two cooperating work rolls. The inventive roll stand can be in particular a 6-high, a 20-roll, or a Z-high roll stand.
It is generally known that the work rolls mounted in a stand to roll the selected in-process stock—and the back-up rolls, which are usually also provided—can be arranged so that the “lower” rolls in the roll stand are fixed in place in a defined position in their chocks, so that a pass line is defined for the in-process stock. The “upper” rolls, however, are mounted so that they can be adjusted in the vertical direction to set the size of the roll gap between the two work rolls. Whereas appropriate adjusting means, which can be used to position the rolls in the desired or required vertical position, are therefore known for the “upper” rolls, this is not true for the “lower” rolls, because these should and must be unable to move vertically.
With respect to the position of the rolls in the roll stand, a great deal of effort is always expended to keep them as parallel to each other as possible, which is necessary not only to guarantee the production of rolled stock of sufficient quality but also to ensure the optimal operation of the devices downstream from the roll stand (e.g., deflecting rolls or coiling units). If the rolls are not parallel, the way in which the tension in the strip is distributed during the rolling process becomes distorted, and damaging axial forces develop in the roller bearings, which can lead to a loss of quality and increased wear.
When a roll stand is being designed, appropriate efforts are therefore made to ensure the parallelism of the rolls. The problem here is that, because of the size of the necessary components (which can be up to 20 m high and weigh up to 300 tons), the limits for the achievable accuracies and tolerances are quickly reached from an economic standpoint. During the installation of the slide plates, thrust pieces, chocks, and other necessary components, the tolerances add up to a largest possible and a smallest possible value.
In the normal case, therefore, the upper back-up roll is moved vertically together with the work roll to regulate the thickness (setting of the roll gap). During this process, the lower back-up roll and work roll remain in the position previously set before the start of rolling. The lower work roll is therefore held fixedly in place, and so that it can be positioned accurately, shims or movable auxiliary adjusting devices (adjusting wedges or spindles) are placed underneath. Because of the additive nature of the tolerances, however, the rolls can be out of parallel by up to 0.5 mm/m. Such lack of parallelism affects the rolling process, because other automatic controls such as the flatness control circuit depend on the measurements of the tension distribution over the cross section of the strip.
The present invention is therefore based on the goal of proposing a method which makes it possible to ensure that the rolls are precisely parallel, wherein both manufacturing tolerances and the lack of parallelism caused by different degrees of wear, which is another factor affecting the horizontal position of the rolls, can be compensated, as a result of which the rolling process can be more easily controlled.
The way in which the invention achieves this goal is characterized in that the method comprises the following steps: